A. Field of the Invention
The present invention relates generally to mud pump pistons, and more particularly to a single acting mud pump piston having a multi-component flange and hub assembly.
B. Description of the Prior Art
Mud pumps are used in the oil and gas drilling industry for circulating drilling fluids, which are commonly and collectively referred to as mud. Mud pumps are positive displacement type pumps that include pistons mounted on reciprocating rods within cylindrical sleeves or liners.
Historically, the first mud pumps were of the duplex type. Duplex pumps include a double sided piston and cylinder arrangement which is adapted to pump in both directions of reciprocation. Duplex pump pistons include a unitary forged piston body which includes a central flange with hubs extending axially from both sides of the flange. Piston rubbers are mounted on the hubs in contact with the flange. The piston rubbers are held on to the piston body by a retainer plate and a snap ring.
More recently, there have been developed single acting multiplex mud pumps, which pump in a single direction of reciproction. Single acting multiplex mud pump pistons are, in effect, duplex mud pump pistons cut axially in half. Indeed, certain manufacturers refer to multiplex mud pump pistons as "half-pistons." More specifically, single acting multiplex mud pump pistons include a unitary forged piston body, which includes a unitary flange with the hub extending axially from one side thereof, and a piston rubber which is retained on the hub in contact with the flange by a retainer plate and snap ring.
There are numerous disadvantages inherent in the construction of presently available mud pump pistons. There are a number of sites that are subject to wear, but at differential rates. The rubbers are most subject to wear and therefore have the shortest expected life of the components of the piston. It would be advantageous to be able simply to replace the rubber periodically. However, the metal parts of the piston are also subject to wear.
A primary wear site is the periphery of the piston body flange, which over time becomes worn down. As the periphery of the piston body flange wears, the rubber has an increased tendency to flow or extrude between the piston body flange and the cylinder wall, thereby leading to failure of the rubber. Another wear site in the piston body assembly is in the snap ring and retaining groove. As the piston reciprocates, the snap ring works back and forth in the groove causing wear to both. As the snap ring and groove wear, the movement therebetween increases and thereby increases the wear. Also, increased movement of the snap ring with respect to the groove causes increased movement and wear of the rubber. When rubbers are replaced, it is common also to replace the retainer plate and snap ring. However, because of the wear to the snap ring groove, replacement of the snap ring does not return the piston to its original tolerances. Thus, replaced snap rings and rubbers have shorter lifes than originals.
A further site of wear or failure is in the piston body itself, primarily at the connection between the flange and the hub. Stresses due to bending of the flange are concentrated at the connection with the hub, which stresses in some cases lead to cracks in the piston body. Additionally, fluid sometimes is able to flow between the rubber and the hub, thereby leading to washout of the hub. Since the piston body is a unitary forging, if any part thereof, i.e. flange, hub, or snap ring groove, is worn, damaged, or out of tolerance, the entire piston body must be replaced.
It is an object of the present invention to provide a single acting mud pump piston that overcomes the shortcomings of the prior art. It is a further object of the present invention to provide a single acting mud pump piston that maximizes the operating life of the various components thereof. It is a further object of the present invention to provide a single acting mud pump piston that is economical to produce and maintain. It is a further object of the present invention to provide a single acting mud pump piston that may be repaired or reconditioned by replacing only the worn parts.